1. Field of the Invention
The present invention relates in general to a composite type magnetic head core slider for a rigid or hard magnetic disk drive, in which a core chip with a writing/reading portion is integrally positioned and fixed in a slider body having air-bearing portions, and a method of manufacturing such a magnetic head core slider. More particularly, the present invention is concerned with techniques for effectively improving the accuracy of a magnetic gap depth of the core chip and/or the flatness of the head core slider surface having the air-bearing portions, to assure high operating reliability of the head core slider.
2. Discussion of the Related Art
As an air-bearing or flying type magnetic head core slider for a rigid magnetic disk drive device, there is known a so-called "composite type" head core slider, which consists of a slider body and a core chip that are prepared independently of each other. The slider body has air-bearing portions, while the core chip has a writing/reading portion for writing and reading information on a magnetic disk. The slider body and the core chip are integrally assembled into the magnetic head core slider. This composite type magnetic head core slider, which is distinguished from a monolithic type, has a smaller thickness at the writing/reading portion and an accordingly lower inductance value of the writing/reading portion, and features improved operating characteristics for high-frequency writing and reading of information, as compared with the monolithic type.
An example of a known method of manufacturing such composite type magnetic head core slider is illustrated in FIGS. 15(a), 15(b) and 15(c). Described specifically, the head core slider consists of a slider body 40 and a core chip 50 which are prepared independently of or separately from each other. As shown in FIG. 15(a), the slider body 40 has two air-bearing portions 42 in the form of two parallel rails formed on an upper surface thereof, and a coil-winding groove 44 and a slot 46 formed at one of the opposite ends thereof as seen in the direction of relative movement of the slider body 40 and a magnetic disk, namely, in the direction of extension of the air-bearing portions 42. The slot 46 is aligned with one of the two air-bearing portions 42, and the coil-winding groove 44 is provided for winding a coil on the core chip 50 inserted in the slot 46. As shown in FIG. 15(b), the core chip 50 has a generally rectangular frame structure having a generally rectangular coil-winding aperture 58, and a track portion 56 which has a magnetic gap 54 formed therethrough and open to the coil-winding aperture 58. The magnetic gap 54 is filled with a protective glass filler 52. The track portion 56, which is separated by the gap 54 into two parts, is shaped by suitable machining so that the track portion 56 has a desired height dimension. The core chip 50 thus constructed is inserted and positioned in the slot 46 of the slider body 40, and a glass rod 60 is placed in contact with the track portion 56 and the adjacent portion of the slider body 40, as shown in FIG. 15(c). The glass rod 60 is then heated to a molten state so that the core chip 50 is bonded to the slider body 40 by a glass filler 61 (FIG. 16). Subsequently, the upper surfaces of the air-bearing portions 42 are ground concurrently with the track portion 56 of the core chip 50, so that the magnetic gap 54 has a predetermined depth value. Thus, a composite type magnetic head core slider 62 as shown in FIG. 16 is produced. The grounding operation to establish the predetermined depth of the magnetic gap 54 will be referred to as "gap depth grinding" where appropriate.
According to the known method of manufacture of the magnetic head core slider 62 as described above, it is difficult to achieve accurate measurement of the depth value of the magnetic gap 54 (which is a distance between the sliding surface or upper surface of the track portion 56 and the upper edge of the coil-winding aperture 58) during the gap depth grinding, in the presence of the glass filler 61 which fills a bottom or lower end portion of the magnetic gap 54 adjacent to the upper end of the coil-winding aperture 58. Consequently, it is difficult to establish the desired depth value of the magnetic gap 54 (hereinafter referred to as "gap depth" where appropriate) by the gap depth grinding. This means a potential problem that the magnetic heads of the individual head core sliders produced suffer from a considerable variation in the operating characteristics.
The magnetic head core slider 62 shown in FIG. 16 suffers from another potential problem which arises from the glass filler 61 exposed to the upper surfaces of the air-bearing portions 42. That is, the glass filler 61 may fuse or corrode due to aqueous and other components in the ambient air, and may cause a tendency of sticking of the magnetic head (head core slider) to a magnetic disk, and consequent deterioration of the operating reliability of the magnetic head.
In the light of the above drawbacks experienced in the prior art, techniques for improving the accuracy of the gap depth of the magnetic head are proposed as disclosed in JP-A-62-185219 and JP-A-62-298916, wherein the core chip is attached to the slider body such that the core chip protrudes a given distance from one end of the slider body in the direction of relative movement between the head core slider and the magnetic disk, so that the magnetic gap portion of the core chip is visible from the outside of an intermediate assembly of the core chip and slider body. This arrangement facilitates the measurement of the gap depth of the magnetic head. JP-A-62-298912 proposes the use of a core chip which has a chamfered region formed at an upper part of the magnetic gap portion, so that the chamfered region can be used to measure the gap depth of the core chip after it is fixedly positioned in the slider body. Described in detail, the length of the chamfered region is measured while the core chip is subjected to the gap depth grinding operation, and the grinding operation is completed when the measured length of the chamfered region coincides with a value corresponding to the desired gap depth. This technique permits improved accuracy of the gap depth value.
In the conventional methods of manufacturing the composite type magnetic head core slider with improved accuracy of the gap depth as discussed above, the core chip is positioned in alignment with one of the air-bearing portions (air-bearing portions 42 as shown in FIG. 16) or a center rail between the air-bearing portions. Therefore, a glass filler for bonding the core chip to the slider body is necessarily exposed on a sliding surface of the head core slider on which a magnetic disk rotates in an air-bearing or flying fashion. When the rigid magnetic disk drive device is at rest, the magnetic disk at rest may contact the glass filler, whereby the magnetic head core slider still suffer from a possibility of sticking to the magnetic disk. Further, the track portion of the core chip is finished or finally shaped before the core chip is attached to the slider body, and the gap depth grinding is effected on the core chip attached to the slider body, namely, after the track portion is finally shaped. Accordingly, the width of the track portion may fluctuate or deviate from the nominal value, depending upon the amount of the gap depth grinding, leading to a variation of the operating characteristic of the magnetic head. The method disclosed in JP-A-62-298912 in which the core chip has the chamfered region for measuring the gap depth also suffers from a problem that the chamfered region provided on the track portion, which constitutes a part of the sliding surface of the head core slider, adversely influences the sliding or air-bearing property of the head core slider with respect to the magnetic disk and the characteristics of the magnetic head. Thus, the provision of the chamfered region is never desirable.
On the other hand, JP-A-63-292414 proposes a composite magnetic head core slider of air-bearing or flying type, in which the core chip is fixedly positioned between left and right air-bearing portions formed on the slider body, after the track portion of the core chip is finally shaped so as to have a relatively small width. The core chip should be positioned with respect to the slider body such that the track portion of the core chip has the same height as the air-bearing portions of the slider body, for uniform air-bearing property over the entire sliding surface of the head core slider with respect to the magnetic disk. Further, utmost cares should be exercised to protect the thin-walled track portion of the core chip when the core chip is positioned relative to the slider body. Thus, assembling of the slider body and the core slider required a cumbersome procedure. If this procedure is replaced by a gap depth grinding operation to simultaneously grind the air-bearing portions and the track portion so that the air-bearing and track portions have the same height dimension, the width of the track portion may fluctuate depending upon the specific amount of the gap depth grinding.
The composite magnetic head core slider shown in FIG. 16 suffers from a further problem which may arise from buckling, warpage or flexture of the slider body during the manufacture. Described specifically, the coil-winding groove 44 is formed to a predetermined depth through one of the opposite end portions of the slider body 40, such that the groove 44 is open on the appropriate end face of the slider body and separates the corresponding end portion of the slider body into opposed two thickness portions. These two thickness portions, which are disposed on the opposite sides of the groove 44, are connected by the core chip 50, at local parts of the slider body 40 which define the slot 46 in which the core chip 50 is received as indicated in FIG. 16. Accordingly, the parts of the opposed thickness portions of the slide body 40 which are relatively remote from the core chip 50 or slot 46 tend to undergo buckling, warpage or flexture. Such buckling or flexture at the thickness portion on the side of the air-bearing portions 42, in particular, deteriorates the flatness of the air-bearing surfaces of air-bearing portions 42, and have an adverse influence on the air-bearing property of the head core slider and the operating characteristics of the magnetic head. This deterioration of the flatness of the air-bearing portions 42 is serious in view of a recently increasing need for minimizing the flying height of the magnetic disk (i.e., distance between the air-bearing surfaces of the slider body 40 and the surface of the magnetic disk), in an attempt to achieve high-density recording of information on the magnetic disk by the magnetic disk drive.
Publication No. 63-87606 of unexamined Japanese Utility Model Application proposes the use of a reinforcing member disposed within the coil-winding groove in the slider body of a composite type magnetic head core slider. The reinforcing member reinforces the end portion of the slider body remote from the core chip, to thereby improve the flatness of the air-bearing portion. However, the proposed provision of the reinforcing member requires a cumbersome procedure to fix the reinforcing member within the coil-winding groove. If the reinforcing member is formed as an integral part of the slider body, it would be difficult to form the coil-winding groove, which has a complicated configuration.